My sister says I cannot use the word Quack

I used the word "Quack" in an off the cuff fashion in an email to my siblings to refer to a doctor. My sister is a doctor and says that this is offensive and that I should desist from using the word. It is a jolly good job that, after an exhausting 38 hour week to get into the top 3% of wage earners, she does not have the time and energy to read my work.

I shall stop using the word quack henceforth. Do you think that, in family correspondence, I should revert to my normal words for those in the medical professsion: viz greedy, overpaid and lazy bastards. Will that go some way to restoring family harmony?

Should my sister wish to refer to my vocation as "hack," a term that, like quack, implies incompetence, but is today used to describe all those employed in the job in a vaguely light hearted way, I shall not be demanding that she desist from doing so.